Department of Medical Zoology, Mie University School of Medicine, Mie, Tsu, Japan.
Department of Molecular Protozoology, Research Center for Infectious Disease Control, Suita, Osaka, Japan.
mBio. 2023 Feb 28;14(1):e0251622. doi: 10.1128/mbio.02516-22. Epub 2023 Jan 9.
Malaria transmission to humans begins with sporozoite infection of the liver. The elucidation of gene regulation during the sporozoite stage will promote the investigation of mechanisms of liver infection by this parasite and contribute to the development of strategies for preventing malaria transmission. AP2-Sp is a transcription factor (TF) essential for the formation of sporozoites or sporogony, which takes place in oocysts in the midguts of infected mosquitoes. To understand the role of this TF in the transcriptional regulatory system of this stage, we performed chromatin immunoprecipitation sequencing (ChIP-seq) analyses using whole mosquito midguts containing late oocysts as starting material and explored its genome-wide target genes. We identified 697 target genes, comprising those involved in distinct processes parasites experience during this stage, from sporogony to development into the liver stage and representing the majority of genes highly expressed in the sporozoite stage. These results suggest that AP2-Sp determines basal patterns of gene expression by targeting a broad range of genes directly. The ChIP-seq analyses also showed that AP2-Sp maintains its own expression by a transcriptional autoactivation mechanism (positive-feedback loop) and induces all TFs reported to be transcribed at this stage, including AP2-Sp2, AP2-Sp3, and SLARP. The results showed that AP2-Sp exists at the top of the transcriptional cascade of this stage and triggers the formation of this stage as a master regulator. The sporozoite stage plays a central role in malaria transmission from a mosquito to vertebrate host and is an important target for antimalarial strategies. AP2-Sp is a candidate master transcription factor for the sporozoite stage. However, study of its role in gene regulation has been hampered because of difficulties in performing genome-wide studies of gene regulation in this stage. Here, we conquered this problem and revealed that AP2-Sp has the following prominent features as a master transcription factor. First, it determines the repertory of gene expression during this stage. Second, it maintains its own expression through a transcriptional positive-feedback loop and induces all other transcription factors specifically expressed in this stage. This study represents a major breakthrough in fully understanding gene regulation in this important malarial stage.
疟原虫对人类的传播始于肝脏中的孢子感染。阐明孢子阶段的基因调控将促进对寄生虫感染肝脏的机制的研究，并有助于预防疟疾传播的策略的发展。AP2-Sp 是一个转录因子（TF），对于孢子或孢子发生的形成至关重要，孢子发生发生在受感染蚊子的中肠的卵囊中。为了了解该 TF 在该阶段转录调控系统中的作用，我们使用含有晚期卵囊的整个蚊子中肠作为起始材料进行了染色质免疫沉淀测序（ChIP-seq）分析，并探索了其全基因组靶基因。我们确定了 697 个靶基因，包括寄生虫在该阶段经历的不同过程中的基因，从孢子发生到发育为肝脏阶段，并代表在孢子阶段高度表达的大多数基因。这些结果表明，AP2-Sp 通过直接靶向广泛的基因来确定基因表达的基本模式。ChIP-seq 分析还表明，AP2-Sp 通过转录自激活机制（正反馈回路）维持自身表达，并诱导所有在该阶段报告转录的 TF，包括 AP2-Sp2、AP2-Sp3 和 SLARP。结果表明，AP2-Sp 存在于该阶段转录级联的顶部，并作为主调控因子触发该阶段的形成。 孢子阶段在从蚊子到脊椎动物宿主的疟疾传播中起着核心作用，是抗疟策略的重要目标。AP2-Sp 是孢子阶段的候选主转录因子。然而，由于在该阶段进行全基因组基因调控研究存在困难，其在基因调控中的作用研究受到阻碍。在这里，我们克服了这个问题，揭示了 AP2-Sp 作为主转录因子具有以下突出特征。首先，它决定了该阶段基因表达的 repertoire。其次，它通过转录正反馈回路维持自身表达，并诱导该阶段特异性表达的所有其他转录因子。这项研究代表了全面理解这一重要疟原虫阶段基因调控的重大突破。
